A wide variety of products are manufactured from polyurethanes such as shoe soles, automotive seats, abrasion resistant coatings, oriented strand board, and door panels just to name a few. In most, if not all, of these applications isocyanate is reacted with one or more isocyanate reactive materials such as polyols, polyamines, and ligno-cellulose. Other materials may be added to the reaction mixture such as catalysts, fire retardants, blowing agents, water, surfactants, and filler as a few examples.
To meet the needs of a particular application, the isocyanate, isocyanate-reactive material, and other additives, if used, can be tailored with remarkable accuracy. For example, polyurethane systems may be tailored to produce closed cell rigid foams such as those used as insulation in buildings and appliances; open celled flexible foams such as those used as cushioning and sound absorbing materials in automotive, furniture, and bedding; elastomers such as those used in footwear, sports equipment, and industrial applications; fiber reinforced composites that may be use in automotive, aerospace, and household applications; coatings such as those used in automotives, floors, and bridges; adhesives which may be used in composite wood products and flexible packaging; and sealants and encapsulants that may be used in construction and automotive.
Polyurethane versatility is also due to the ease with which products are made. For instance, polymerization may take place during formation of the final article, which gives the processor the ability to change and control the nature and the properties of the final product. The tailoring ability and ease of fabrication give an enormous cost-performance advantage to polyurethane-based products and are the key reasons behind its remarkable industrial success over the last four decades.
Although number of different types of polyurethane products, each with its own unique properties, is remarkable, cost-performance may be improved by adding nanoparticles such as clay nanoparticles to polyurethane systems to form polymer nanocomposites. Polyurethanes made with nanoparticles may exhibit property enhancements beyond those possible with traditional, micron or higher sized additives.
To make a polymer nanocomposite with improvements in properties at relatively low nanoclay content, the nanoclay should be uniformly dispersed in the polymer matrix. One challenge to making such a nanocomposite is to separate or delaminate the smallest, indivisible clay nanoparticles such as platelets and to uniformly disperse the platelets in the polymer all at a relatively low cost.
Clays can be organically modified to aid in delamination and/or dispersion. For example, in each of U.S. Pat. No. 6,518,324, U.S. Pat. Application No. 2007/0072991, U.S. Pat. Application No. 2007/197709, U.S. Pat. Application No. 2007/0227748, and G. Harikrishnan, T. Umasankar Patro, and D. V. Khakhar, Polyurethane Foam—Clay Nanocomposites: Nanoclays as Cell Openers, Ind. Eng. Chem. Res., 2006, 45, 7126-7134 the clay was organically modified to delaminate clay platelets. Generally, clays can be organically-modified by associating an ion incorporating a lipophilic group with the ionic charge on the clay surface. The use of organically modified clays, however, significantly increases the cost of the finished product and potentially decreases or eliminates certain polymer properties such as fire resistance. Although the above-referenced patents and publications were directed toward polyurethanes, Polymer Nanocomposites, Processing, Characterization and Applications; Thermoset Nanocomposites for Engineering Applications and the article “Twenty Years of Polymer-Clay Nanocomposites,” by Okada et al., Macromolecular Materials and Engineering, 2006, 291, 1449-1476 indicate that organic modification of clays is also used for forming nanocomposites with other polymers.
In addition to organically modifying clays, a solvent may used to aid with nanodispersion. The use of solvents, however, has limited applicability and compatible polymer-silicate solvent systems are not always available. Furthermore, solvent removal can be very expensive and environmentally damaging.
Another technique that is gaining attention is direct polymer melt intercalation. With direct polymer intercalation, the polymer and silicate are mixed and the mixture is heated above the softening point of the polymer, usually using an extruder. This technique, however, has limited applicability to polyurethane products as most of them are thermosets.
Thus there is a continuing need for making polyurethane nanocomposites with reduced or eliminated organic modification by lipophilic counter ions of the clay, use of solvents, or both.